Oscillator



Aug. 30, 1938.

H. R. MEAHL OSCILLATOR Filed April 16, 1956 Inverrtor:

Harry RM ahl,

1 76 44 5. Hi Attorney.

Patented Aug. 30, 1938 UNITED STATES PATENT OFFICE Electric Company,

. York Application April 16,

4 Claims.

My invention relates to crystal controlled oscillators and it has for one of its objects a novel method and means for controlling the voltage impressed on the crystal thereof.

In high frequency apparatus of the type which includes a crystal controlled oscillator, it is highly desirable and frequently necessary to provide either some means for limiting the amount of feed-back in the oscillating circuit or else to providesorne means for limiting the voltage impressed on the crystal. Excessive feed-back with the resultant excessive voltage impressed on the crystal of an oscillating circuit tends to create wave disturbances, causes poor frequency sta-' bility and often causes blocking of the oscillator. When the oscillating circuit is designed to operate at extremely high frequencies, excessive voltage on .the crystal frequently causes disintegration of the crystal because of the small crystal dimensions necessary for high frequency operation; These excessive voltages occur because-the feed-back through the electron disas above 6 megacycles.

charge device ofthe oscillator increases as a function of frequency. Various satisfactoryarrangements' have been provided for limiting feed-back and the voltage impressed on the crystal of an oscillating circuit where the circuit has been designed for operation on so-called long waves and for ordinary short Waves.

No satisfactory arrangement has been provided,

however, for controlling feed-back or for limiting the voltage impressed on the crystal of an oscillating circuit which is designed to operate at extremely high frequencies, such, for example,

It is, therefore, an object of my invention to provide a novel means for limiting the voltage impressed across the crystal of a crystal controlled oscillator of the type which is designed to operate at extremely high frequencies. a

The novel features-which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure thereof illustrates a crystal controlled oscillator constructed in accordance with my invention.

Referring to the drawing, I have illustrated at i an electron discharge devicehaving an anodev 2, a cathode 3, and a control electrode 4. 'An output impedance 5, comprising an inductance 6 a corporation of New 1936, Serial No. 74,658 (01. 250--36) and a variable capacitor 1, is connectedbetween anode 2 and cathode 3. Anode 2 is also connected to a suitable source of high potential (indicated as B) through the usual radio frequency choke 8, the latter being employed to keep the potential source free of radio frequency oscillations. The usual blocking condenser 9 is connected in the anode return 'circuit to prevent the high unidirectional voltage of the potential source from being impressed on cathode 3. Control electrode 4 is given a suitable bias by means of the fixed biasing. resistor H]. A transmission line ii, having uniformly distributed inductance and capacity, and being substantially a whole number of half wave lengths long at the desired operating frequency, is connected between control electrode 4 and cathode 3, for reasons which will presently be explained.

The operating circuit thus far described is of the so-called tuned-plate tuned-grid type in which the tuned circuit for the grid or control electrode is formed by transmission line II. When transmission line H has a length equal to a whole number of half wave lengths at the op erating frequency, a standing Wave M is established thereon upon energization'of discharge device I.

.In accordance with my invention a piezo electric crystal I2 having suitable electrodes 13 is connected across transmission line H at a point somewhere between a nodal point of potential and an anti-nodal point of potential of standing wave i l on transmission line H. By varying the point at which piezo electric crystal I2 is connected to transmission line II with respect to the standing wave established thereon, it is apparentthat the voltage impressed on crystal i2 may be varied from zero to the maximum voltage of standing wave l4. Hence, a simple means is provided for controlling the voltage which is impressed across the piezo electric crystal.

It should be understood that piezo electric crystal l2 constitutes the dominant stabilizing means of the oscillator and that transmission line I l is used primarily for obtaining a standing wave system to which crystal l2 may be selectively connected. For this reason, transmission line i I may be much shorter than that necessary when it is used as a frequency stabilizing means. It has been found that a line substantially one and one-half wave lengths long gives highly satisfactory results when used in an oscillator of the type illustrated in the drawing.

In order to hold the standing wave pattern constant it is sometimes desirable to connect a resistance H: such as an incandescent lamp across transmission line H at a nodal point of potential. Whenever standing wave I4 tends to shift one way or the other along the line, a voltage is impressed across resistor l5 and a short circuit is placed across the line. This tends to maintain the nodal points of standing wave M at fixed points along line H.

The operation of my device is as follows. The filament of electron discharge device I is energized from a suitable source of potential (not shown) and the high potential source is connected between anode 2 and cathode 3. By reason of the feed-back from anode 2 to control electrode 4 in discharge device I, high frequency oscillations are established. Crystal I2 is moved along transmission line H until a point is reached where there is just sufiicient voltage impressed across its electrodes l3 to maintain oscillations. It will be noticed that varying the position of crystal l2 along transmission line ll does not in any way vary the amount of feed-back in discharge device I. This, however, is unnecessary since the voltage impressed across crystal |2 is now limited to a value which will not cause any of the disadvantages previously referred to.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications may be made both in the circuit arrangement and in the instrumentalities employed, and I therefore contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

=1. In a tuned plate crystal controlled oscillator, the combination of an electron discharge device having an, anode, a cathode, and a control electrode, an output impedance connected between said anode and said cathode, a source of potential connected between said anode and said cathode, a resonant transmission line connected between said control electrode and said cathode, said transmission line being a whole number of half wave lengths long at a desired operating frequency, a piezo electric crystal, and means for selectively connecting said crystal across said line, thereby selectively to control the voltage impressed across said crystal.

2. A crystal controlled electron discharge oscillator comprising an electron discharge device having an anode, a cathode and a control electrode, a resonant transmission line connected between said control electrode and said cathode,

said line being substantially a whole number of half wave lengths long at a desired operating frequency, an output impedance connected between said anode and said cathode, and a piezo electric crystal connected across said transmission line at a point intermediate a nodal point of potential and an anti-nodal point of potential of said line.

3. In a crystal controlled oscillator, the combination with an electron discharge device having an anode, a cathode, and a control electrode, of means for energizing said discharge device, an oscillatory circuit connected. between said anode and said cathode, a piezo electric crystal, means comprising a transmission line connected between said control electrode and cathode for producing standing waves, and means to connect selectively said crystal across said line at a point thereof of suitable potential for excitation of said crystal.

4. In a crystal controlled oscillator, the combination with an electron discharge device having' an anode, a cathode, and a control electrode, of means for energizing said discharge device, an oscillatory circuit connected between said anode and said cathode, a piezo electric crystal, means comprising a transmission line connected between said control electrode and cathode for producing standing waves, means to connect selectively said crystal across said line at a point thereof of suitable potential for excitation of said crystal, and a resistance connected across saidline on the opposite side of said crystal from said discharge device and at a nodal point of potential of said line. L

HARRY R. MEAHL. 

